I don't think I had this issue in CS3. In CS6, say I have a stroke of 1.25pt for a straight line, when I save it for web, the stroke will be the same as 1pt instead. I tested and going up to 1.37pt has the same effect. I feel like other strokes are averaging out to other values too, making it difficult to make lines look slightly thicker. Anyone familiar with this issue or know how to fix it?
Align to pixel grid is OFF both for new documents and for the objects. And the only reason I noticed this issue was because I edited a graphic from 5 years ago that I did in CS3 and noticed the lines looked wrong. New documents have the same issue.
It's as if Illustrator is forcing align to pixel grid when saving for web. I can even see the 1.25pt lines look normal for a split second in save for web preview and then changing to 1pt.
Edit: I've added screenshots to try to show what's going on. The first picture is what I see on the artboard. The second picture is what I see in Save for Web preview, which is how it looks after saving. Export and Save for Office seem to work fine, it's just Save for Web that's messed up.
Edit2: I'm using Windows 10 64-bit.